It is known from German Patent 24 14 576 (see also U.S. Pat. No. 3,997,700) to provide a fire-retardant mass which can be incorporated between two glass panes in an intervening space therebetween, by reacting a water-soluble aluminum salt and an inorganic acid to produce a hydrated-metal salt which forms the fire-retardant mass upon drying.
In practice, therefore, when the fire-retardant mass is introduced between glass panes and dried, e.g. in hot air, so that the water required for the foaming of the product, which s present as water of hydration, is driven or destroyed, the product, when subjected to fire, can foam in place to form a barrier to further penetration of heat or fire, absorb substantial amounts of heat and otherwise act as a fire-retardant mass.
In the aforementioned patent the aluminum salt is hydrated aluminum chloride and the inorganic acid is phosphoric acid so that the fire-retardant mass consists predominantly of hydrated aluminum phosphate.
A problem with this product is that, even in its finished form, it can contain quantities of chlorine from which chlorine gas can be liberated even upon drying. Chlorine gas has an environmental hazard both at the workplace and at the site at which the glazing is installed.
In addition, the resistance of the glazing to aging and its optical clarity under exposure to sunlight and heat leaves much to be desired. Furthermore, the fire resistance, foaming characteristics and other properties of the product appear to invite improvement.